A ready-mixed concrete agitating truck is equipped with a concrete agitating drum for agitating and discharging ready-mixed concrete supplied from a hopper or the like. The agitating drum is driven by a hydraulic motor.
JP2000-272405A, published by the Japan Patent Office in 2000, proposes a hydraulic drive circuit for such a concrete agitating drum.
In this hydraulic drive circuit, the hydraulic motor is supplied with pressurized oil from a variable capacity hydraulic pump. The variable capacity hydraulic pump comprises an actuator which varies a pump discharge flow rate. The actuator operates in response to a pump discharge pressure of the variable capacity hydraulic pump.
A load sensing valve regulates the pump discharge pressure supplied to the actuator, thereby maintaining a differential pressure between the pump discharge pressure and a load pressure under which the hydraulic motor operates at a constant value. When the differential pressure is maintained at a constant value, the flow rate of the pressurized oil supplied from the variable capacity hydraulic pump to the hydraulic motor is also maintained at a constant value. As a result, even when a rotation speed of the variable capacity hydraulic pump, which is driven by an internal combustion engine varies, the rotation speed of the agitating drum is maintained at a constant rotation speed.